Rapidly unfolding natural or man-made disasters or emergencies such as bushfires, cyclones, and tsunamis have the potential to affect large numbers of people in a short time, with consequential risk to life and property. Such emergencies, which are often of long duration (several days), can evolve unpredictably, so that the population affected by the emergency can change at short notice. The risk to life and property is greatly reduced if people likely to be affected are made aware of the threat and informed of preventive or palliative measures (e.g. evacuation, retreat to shelters) in advance of the actual onset of the emergency.
However, people do not always gather information on an evolving emergency in the same manner. Some people may monitor a certain television station, others a certain radio station, some the Internet, and some may rely on word of mouth. In addition their monitoring may not be constant, but rather intermittent. This presents a challenge to authorities wishing to keep people informed about an emergency developing rapidly in their area of responsibility.
Known solutions including sirens and loudspeakers in public places either fail to reach many affected people or lack informative content. It is expensive and perhaps impractical to ensure wide coverage by broadcasting constant emergency update bulletins on every channel of every possible broadcast medium. Also for a potentially affected person, it can be exhausting to remain alert for updates on an evolving emergency day and night for days on end. These problems may also be exacerbated in remote or Third World regions where communications resources may be limited.